Very few of the heroes and villains made famous in the wars of the past decade are women. Of the scant exceptions, two of the most fascinating are the subjects of Deborah Scroggins’s thoughtful double biography, “Wanted Women.”

One is Ayaan Hirsi Ali, the Somali-born thinker and neoconservative darling; the other is Aafia Siddiqui, a Pakistani neuroscientist who, in 2010, was sentenced to 86 years in prison for her assault on American personnel in Afghanistan. She is known as Al Qaeda’s highest-ranking female associate.

The popular imagination has cast Hirsi Ali as a firebrand, clad in a satin evening gown and flanked by bodyguards as she denounces Islam. The diminutive Siddiqui is a firebrand of a different sort. She wears a burqa and totes vials of chemical weapons in her purse while denouncing the West. Yet the issue of who these self-made women actually are — and who they aren’t — remains deeply contested.

In 1992, Hirsi Ali fled from Africa to the Netherlands, where she won a bid for asylum and Dutch citizenship. She was elected to the Dutch Parliament in 2003. Thanks to her speeches, articles and participation in a short film called “Submission,” which depicted verses of the Koran on a woman’s naked body, as well as to her two successful autobiographies, “Infidel” and “Nomad,” she has been embraced both by many feminists and many on the American right. She argues that “Islam is backward,” and that its values must be stamped out before they overwhelm the West. Her most vociferous supporters — including her husband, the historian Niall Ferguson — consider her to be one of the staunchest defenders of freedom in our time. The late Christopher Hitchens once wrote, “The three most beautiful words in the emerging language of secular resistance to tyranny are Ayaan Hirsi Ali.” Her critics, however, claim that her views are simplistic and, more harshly, that she is an opportunist.

Siddiqui is similarly polarizing. She traveled from her home in Karachi to the United States in 1989 to pursue her education, which she did at M.I.T. and Brandeis University. She eventually married Amjad Khan, a doctor from Karachi, bore him three children and completed the requirements for her master’s degree and Ph.D. in neuroscience in less than four years. At the same time she was embracing the most millenarian principles of jihad. In 2002, after the F.B.I. had begun investigating her for links to Al Qaeda, she returned to Pakistan and soon disappeared, only to be spotted in Ghazni, Afghanistan, along with her 12-year-old son in 2008. Maps, toxic chemicals and diagrams for making bombs were found in her possession, and after a tussle with American forces during which she was shot in the stomach, she was taken into custody. Her defenders — including her family and many Pakistanis — believe she is a devout mother and martyred hero sentenced to American prison because she is a Muslim. The United States government contends she is a terrorist.

In “Wanted Women,” Scroggins traces the lives of Hirsi Ali and Siddiqui from their earliest childhoods down to the present. Hirsi Ali continues to live in the United States; Siddiqui now resides in Fort Worth, Tex., where she is incarcerated at the Federal Medical Center Carswell and receiving psychiatric treatment.

Alternating between the two women, Scroggins explores what she calls “their weird symmetry,” examining how the forces of contemporary history — war, poverty, colonialism and politics — have forged these “icons of the war on terror.” She writes: “When it came to dealing with the crises of Islam, they were mirror opposites, but there were hints in their complicated backgrounds that each woman might have gone in a very different direction, perhaps even to the extent of Aafia Siddiqui becoming a Westernizing feminist and Ayaan Hirsi Ali becoming a militant Islamist.”

These linked narratives may seem at first to be simply a reductive gimmick based on the fact that both women were born as Muslims and educated in the West. Yet Scroggins, who has been an award-­winning foreign correspondent for The Atlanta Journal-Constitution, is a thorough reporter and an astute analyst of global events. Because of her willingness to introduce readers to over a century of Islamic theology and politics, a book that might have been a facile juxtaposition of two very different individuals is actually much more than the sum of its parts. “I had felt for years,” she writes, “that the suppression of women was as basic to the ideology of radical Islam as racism had been to the old American South or as anti-Semitism was to Nazi Germany.”

To tell Siddiqui’s story, Scroggins begins in 19th-century India. She explains how Deobandism, an Islamic anticolonial movement that started about two centuries ago, has had a profound (and underinvestigated) impact on the politics of contemporary Pakistan.

Eloquence, courage and historical command are some of Scroggins’s well-known talents — ones she exhibited in her first book, “Emma’s War.” There, she chronicled the life and death of Emma McCune, a British aid worker in Sudan who became the wife of a warlord, while simultaneously providing one of the best histories of Sudan’s complicated civil war. Like “Wanted Women,” “Emma’s War” was a kind of double biography, but with Scroggins setting herself in opposition to McCune.

“Emma’s War” raised such high expectations, however, that “Wanted Women” seems a bit of a disappointment. Though Scroggins is a master at using herself to reflect the horror or mystery unfolding around her, here we get only fleeting glimpses of her as a character. One misses her observer’s guidance.

There is one exception. While investigating Siddiqui’s rumored arrest by Pakistani intelligence in 2005, Scroggins makes a grave mistake: unthinkingly, she forwards an e-mail from a Pakistani source to Siddiqui’s American lawyer. By exposing the source’s identity, Scroggins puts him in danger. He writes an anguished e-mail to Scroggins, saying “u have no idea that u have risked my life.” It’s a chilling reminder of the risks that reporters in Pakistan, among others, face while doing their jobs.

As Scroggins concedes from the start, she has never spoken to either of her two subjects, and she adds: “I came to see my enforced distance from both women as a blessing in disguise.” This could appear to be a convenient rationalization for what many would consider a serious limitation, yet Scroggins is so talented a storyteller that it is easy to forget her lack of contact with Hirsi Ali and Siddiqui as she moves deftly through their remarkable lives, capturing human qualities that help us get behind each woman’s public image.

It is undeniably a risky undertaking to attempt to write the biography of not one but two living figures who were unwilling to participate in the endeavor. But Scroggins, with her journalistic doggedness, does a remarkable job of reporting and reconstruction, and “Wanted Women” serves as a valuable contribution to contemporary history, recounting two ways in which a modern woman’s identity can be hers for the making — even if the outcome is tragic.

WANTED WOMEN

Faith, Lies, and the War on Terror: The Lives of Ayaan Hirsi Ali and Aafia Siddiqui

By Deborah Scroggins

Illustrated. 539 pp. Harper/HarperCollins Publishers. $27.99.

Eliza Griswold, a senior fellow at the New America Foundation, is the author of “The Tenth Parallel.”

A version of this review appears in print on January 29, 2012, on page BR17 of the Sunday Book Review with the headline: Firebrands. Today's Paper|Subscribe